I have been using big organic fertilizer spikes 5-2-4 with micros. 3 spikes per plant every month in my greenhouse potted bananas. The results have been outstanding. A company I consult for in Washington started manufacturing the spikes last year and my greenhouse and an organic tomato growers greenhouse were used as test plots. I listed them on my eBay store, here's the link if you want to look at them.
Organic Fertilizer Spikes Big Spikes Garden/Greenhouse - eBay (item 350013633444 end time May-08-08 06:43:35 PDT)